Re: [qemu-s390x] [Qemu-devel] [PATCH v1 31/41] s390x/tcg: Implement VECTOR SHIFT LEFT DOUBLE BY BYTE

[David Hildenbrand]

On 13.04.19 02:54, Richard Henderson wrote:
> On 4/11/19 12:08 AM, David Hildenbrand wrote:
>> +static DisasJumpType op_vsldb(DisasContext *s, DisasOps *o)
>> +{
>> +    int src_idx = get_field(s->fields, i4) & 0xf;
>> +
>> +    if (src_idx == 0) {
>> +        gen_gvec_mov(get_field(s->fields, v1), get_field(s->fields, v2));
>> +    } else {
>> +        gen_gvec_3_ool(get_field(s->fields, v1), get_field(s->fields, v2),
>> +                       get_field(s->fields, v3), src_idx,
>> +                       gen_helper_gvec_vsldb);
>> +        return DISAS_NEXT;
> 
> You could also expand this inline using your new extract2 primitive.
> 
>   int i4 = get_field(s->fields, i4);
>   int left_shift, right_shift;
> 
>   left_shift = (i4 & 7) * 8;
>   right_shift = 64 - left_shift;
> 
>   if ((i4 & 8) == 0) {
>       read_vec_element_i64(t0, get_field(s->fields, v2), 0, ES_64);
>       read_vec_element_i64(t1, get_field(s->fields, v2), 1, ES_64);
>       read_vec_element_i64(t2, get_field(s->fields, v3), 0, ES_64);
>   } else {
>       read_vec_element_i64(t0, get_field(s->fields, v2), 1, ES_64);
>       read_vec_element_i64(t1, get_field(s->fields, v3), 0, ES_64);
>       read_vec_element_i64(t2, get_field(s->fields, v3), 1, ES_64);
>   }
>   tcg_gen_extract2_i64(t0, t1, t0, right_shift);
>   tcg_gen_extract2_i64(t1, t2, t1, right_shift);

Trying to understand the magic, left_shift is really only used to to
calculate right_shift, right?

>   write_vec_element_i64(t0, get_field(s->fields, v1), 0, ES_64);
>   write_vec_element_i64(t1, get_field(s->fields, v1), 1, ES_64);
> 
> 
> r~
> 


-- 

Thanks,

David / dhildenb